Polysilazane Thermosetting Polymers for Use in Chromatographic Systems and Applications

ABSTRACT

This invention relates to an amorphous non-glassy ceramic composition that may be prepared by curing, calcining and/or pyrolyzing a precursor material comprising silicon, a Group III metal, a Group IVA metal, and/or a Group IVB metal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/993,168filed Nov. 19, 2004, which claims the benefit of provisional applicationSer. No. 60/523,654, filed Nov. 20, 2003, each of which is herebyincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to an amorphous non-glassy ceramic compositionthat may be prepared by curing, calcining and/or pyrolyzing a precursormaterial comprising silicon, a Group III metal, a Group IVA metal,and/or a Group IVB metal. In particular, the composition is notirreversibly adsorptive for components or fluids that come into contactwith it thereby allowing it to be useful as a passivation coating orfilm for any underlying substrate where it functions as a barrieragainst adsorption of components of the fluid to the underlying surfaceof the substrate. Further, the amorphous non-glassy ceramic compositionfunctions as a highly useful matrix for a particulate adsorptivematerial, and/or as a film for adhering such adsorptive material to anunderlying surface. Still further, the precursor material may comprise apolysilazane, polysiloxane, and particulate adsorptive material forminga fluid-permeable mass useful, for example, as an improved adsorptivebed in pipette tips.

There has been a long-identified need in scientific analyticaltechniques, such as chromatographic applications, to have the ability tocoat a substrate thereby causing the substrate to be non-reactive withrespect to a target analyte that comes into contact with the substrate.In particular, with respect to chromatographic applications, a coatinguseful to provide a barrier against adsorption of components in a fluidto the surface of a vessel, conduit, or device which is in contact withthe fluid. Interactions between the target analyte and the surfaces of avessel, conduit, and/or device may affect analytical results. Thisaffect may be more pronounced in SPME applications where only a veryminute amount of analyte is adsorbed. U.S. Pat. No. 5,192,406 disclosescertain surface-deactivation techniques using polymeric silyl hydrides,siloxanes, silazanes and silicone polymers to deactivate glass orfused-silica CZE capillary columns without eliminating electro-osmoticflow. Further, deactivation of capillary columns for gas chromatographyis also disclosed. However, no discussion is given to parts of thechromatographic apparatus other than the glass or fused silica columns.

Recently, the formation of silicon containing passivation films onvarious substrates has been dominated by techniques such as ChemicalVapor Deposition (CVD), Plasma CVD or wet chemical methods, includingSol Gel. These techniques can be effective, but suffer from severaldrawbacks requiring further improvement.

Silicon containing film forming processes utilizing CVD (e.g., U.S. Pat.No. 6,511,760 and U.S. Pat. No. 6,444,326) often suffer in some or allof the following areas: (1) contamination of the apparatus and substratecaused by formation of silicon particles in the gas phase reaction,thereby reducing production yields and/or requiring post-coatingclean-up; (2) difficulty in obtaining a uniform film on uneven surfacesand/or presence of undesirable substances such as oxides in the film,caused by the gaseous nature of the raw materials; (3) low productivitycaused by low film formation speeds; (4) necessity of complex andexpensive equipment, such as high frequency generators and vacuumequipment; and (5) high reactivity and toxic nature of the gaseous rawmaterials, such as gaseous silicon hydride, requiring appropriatehandling procedures and safety equipment to provide airtight conditions.

Researchers have attempted to produce passivating films from liquidsilicon hydride containing raw materials with limited results.JP-A-29661 recites a process for forming a silicon-based thin film byliquefying a gaseous raw material on a cooled substrate and subsequentlyreacting it with active atomic hydrogen. This process involves complexequipment and is very difficult to control film thickness.

Low molecular weight liquid silicon hydride as a film-forming precursoris disclosed by JP-A-7-267621. However, the process recited isproblematic due to the handling of unstable material and wettabilityproblems associated with substrates of large surface area.

A solid silicon hydride polymer precursor was recited by GB-2077710A.However, the material is difficult to use due to poor solubility incommon solvents.

Further, U.S. Pat. No. 6,503,570 discloses the synthesis ofsilylcyclopentasilane as a liquid film-forming precursor. This materialis decomposed at temperatures below 500° C. and is easily dissolved incommon organic solvents such as toluene, hexane, THF and acetone.Limitations of this approach include the complicated and costlysynthetic procedure and the instability of the material in air.

U.S. Pat. No. 5,853,808 discloses the decomposition ofchloroethylsilsesquioxane into thin ceramic films. Rearrangementreactions are generally conducted under intense UV light with theevolution of highly corrosive hydrochloric acid. Additionally, the highcost of production further limits this family of materials.

Sol Gel technology has been widely used in the formation of silicacontaining films and binder applications for small particles. Generally,the procedure involves the acid hydrolysis of metal alkoxides to formliquid sol solutions used in the above-mentioned applications. Thisliquid precursor technique suffers from limitations such as poor solventcompatibility and substrate wettability. Further, uneven coating andpinhole formation can be major problems along with the inability tocreate stable suspensions of particulate matter. Additionally, Solsolutions can be very unstable resulting in premature gelation and shortshelf life. U.S. Pat. No. 4,277,525 describes a complicated method toeliminate the shortcomings of the technique. Generally, an alkoxysilaneis mixed with a carboxylic acid or anhydride with a pK larger than 4. Athird reactant, a monovalent or divalent alcohol such as methanol,ethanol or ethylene glycol, is added. A reaction accelerator isdescribed as a different carboxylic acid with a pK not exceeding 4. Solformation proceeds over several hours. Precautions are necessary so theexothermic reaction does not raise the temperature of the sol over 50°C. or gelation may occur. Along with the complexity of the Solpreparation, the large amounts of residual carboxylic acid may createwetting problems on some substrates.

To facilitate the handling of adsorbent particles, it may be helpful toagglomerate the particles into shaped forms, beads or the deposition ofthese particles on a substrate. A stable adherent coating of particlesthat resists delamination from the substrate in use may be advantageousfor a variety of reasons, including (1) improvement of surface area toweight ratio; (2) reduction in the total amount of adsorbent required(3); protection of the underlying substrate from aggressiveenvironments; and (4) the geometry of the substrate may be required toprovide strength or form to the adsorbent system. A binding material isneeded that allows for easy suspension of particulates, adequateadhesive properties to a variety of substrates, high stability andinertness in both liquid precursor and ceramic form, low interferencewith adsorbent porosity.

U.S. Pat. No. 5,325,916 and U.S. Pat. No. 6,143,057 both describe a widevariety of binding materials used in the creation of adsorbentstructures composed of fine zeolite materials. Suitable binders include,macroporous clays, silicas, aluminas, metal oxides and mixtures thereof.These types of binding materials may be limited to more durableadsorbents such as zeolites or silicas and may not provide the inertnessrequired for the subsequent desorption of many organic molecules.

Further, U.S. Pat. No. 5,599,445 discloses the use of a siloxane polymeradhesive as a binding material for various adsorbents including alumina,silica, organic polymer adsorbents and zeolites. Adsorbent films may beprepared and used as chromatographic stationary phases for volatileorganic and permanent gas separation. The siloxane material may be usedsuccessfully, but adversely effects pore volume of the adsorbents.Additionally, these polymeric type materials have limited thermalstability resulting in unwanted volatile by products upon decomposition.

The current commercial pipette tips exhibit fracturing of the bedsduring tip usage, and therefore lack sufficient capacity. Also, severalcommercially available tips possess coatings only on the tip walls andtherefore have limited capacity with analyte recovery significantlyreduced.

The present invention seeks to reduce or eliminate the limitations ofknown compositions and methods due to the chemical properties of themacromolecules and decreased production costs allowing for use in avariety of chromatographic systems and applications.

SUMMARY OF THE INVENTION

Among the several aspects of the present invention is the provision ofan adsorptive structure comprising particulate adsorptive materiallodged in a matrix comprising an amorphous non-glassy ceramiccomposition and/or adhered to an underlying surface via a filmcomprising an amorphous non-glassy ceramic composition. The ceramiccomposition comprises an element selected from the group consisting ofsilicon, a Group III metal, a Group IVA metal, a Group IVB metal andcombinations thereof and may be interrupted by nitrogen or carbon atoms.Further, the ceramic composition may be characterized by certainadsorption spectra having characteristic band ranges at varioustemperatures. The particulate adsorbent material is nucleophilic,electrophilic, or neutral and includes carbon, organic polymers,silicas, zeolites, aluminas, metal or ceramic powders, which are lodgedin the ceramic composition such that the particles are accessible tocontact with an analyte contained in a fluid. The underlying surface isselected from the group consisting of glass, metal, plastic, wood,fabric, ceramic or combinations thereof, and includes a chromatographiccolumn.

Another aspect of the invention includes an adsorptive structure whereinthe ceramic composition is derived from an oligomer comprising repeatingunits in which nitrogen is combined with an element selected from thegroup consisting of silicon, a Group III metal, a Group IVA metal, aGroup IVB metal and combinations thereof. The ceramic composition may beprepared by mixing the particulate adsorptive material and the oligomerand heating until the ceramic composition forms.

Further aspects of the invention include chromatographic methods whereina mobile fluid phase containing an analyte may be contacted with astationary phase comprising particulate adsorptive material that islodged in a matrix comprising an amorphous non-glassy ceramiccomposition and/or adhered to an underlying surface via a filmcomprising an amorphous non-glassy ceramic composition, the ceramiccomposition comprising an element selected from the group consisting ofsilicon, a Group III metal, a Group IVA metal, a Group IVB metal andcombinations thereof. The stationary phase may comprise a packing for achromatographic column or solid phase extraction device wherein saidpacking comprises discrete adsorptive bodies. Alternatively, or inaddition, the stationary phase may comprise a ceramic film on theinterior surface of a chromatographic column wherein the particulateadsorptive material is lodged in or adhered to the interior surface viathe film.

Other aspects of the invention include a chromatographic separationdevice comprising a tubular column and, on a wall of said column, a filmcomprising an amorphous non-glassy ceramic composition and a particulateadsorptive material, the adsorptive material being lodged in said filmor adhered via said film to said wall. The non-glassy ceramiccomposition comprises an element selected from the group consisting ofsilicon, a Group III metal, a Group IVA metal, a Group IVB metal, andcombinations thereof.

Another aspect of the invention includes a composite comprising anon-glass substrate and a coating over a surface of the substrateproviding a barrier against adsorption to the substrate of a componentof a fluid in contact with the composite. The coating comprises anamorphous non-glassy ceramic composition that is derived from anoligomer comprising repeating units in which nitrogen is combined withan element selected from the group consisting of silicon, a Group IIImetal, a Group IVA metal, a Group IVB metal, and combinations thereof.The preparation of the non-glassy ceramic coating may comprise theapplication to the surface of the substrate a flowable dispersioncomprising the oligomer followed by heating of the dispersion to form aceramic composition. The non-glass substrates may be selected from thegroup consisting of copper, aluminum, steel, stainless steel, nitinol,bronze, zirconium, titanium, and nickel.

Another aspect of the invention includes a composite comprising a glasssubstrate and a coating over a surface of said substrate providing abarrier against adsorption to the substrate of a component of a fluid incontact with the composite. The coating comprises an amorphousnon-glassy ceramic composition that is derived from an oligomercomprising repeating units in which nitrogen is combined with an elementselected from the group consisting of silicon, a Group III metal, aGroup IVA metal, a Group IVB metal, and combinations thereof. The glasssubstrates may include, for example, inlet sleeves, wool, syringebarrels, sample vials, connectors (such as press-tight, column, andseal), adsorbent trap assemblies and thermal tubes.

Further aspects of the invention include a fluid-permeable masscomprising a particulate adsorbent material dispersed in a matrixcomprising a polysilazane polymer and a polysiloxane polymer; a solidphase adsorptive device comprising a conduit or vessel having aparticulate adsorptive material entrapped therewithin by a bindercomprising a polysilazane polymer and a polysiloxane polymer; and aprocess for preparing a fluid-permeable mass comprising a particulateadsorbent material dispersed in a polymeric matrix comprising preparinga dispersion comprising the particulate adsorbent material in a liquidmedium comprising a solvent, a polymerizable silazane and apolymerization initiator, the polymerizable silazane comprising apolysilazane monomer, a polysilazane oligomer, or a mixture thereof; andpolymerizing the polymerizable silazane to form said fluid-permeablemass.

A further aspect of the invention includes a pipette adapted for solidphase extraction, the pipette comprising a barrel and a tip, the tipcontaining a fluid-permeable mass comprising a particulate adsorbentmaterial dispersed in a matrix comprising a polysilazane polymer.

Another aspect of the invention includes a pipette adapted for solidphase extraction, the pipette comprising a barrel and a tip, aparticulate adsorptive material being entrapped within the tip by abinder comprising a polysilazane polymer.

Still further aspects of the invention include a process for adhering aparticulate adsorptive material to an interior wall of a conduit orvessel comprising establishing a dispersion comprising the particulateadsorbent material within the conduit or vessel, the dispersioncomprising the adsorbent material in a liquid medium comprising asolvent, a polymerizable silazane and a polymerization initiator, thepolymerizable silazane comprises a polysilazane monomer, a polysilazaneoligomer, or a mixture thereof; and polymerizing said polymerizablesilazane to form a binder entrapping said adsorptive material withinsaid conduit or vessel.

A further aspect of the invention includes a method for separating atarget compound from a sample comprising a fluid medium containing saidcompound, the method comprises drawing the sample into a vessel orconduit containing an adsorbent bed, the adsorbent bed comprisingparticulate adsorbent material dispersed in an adhesive matrix orentrapped by an adhesive binder, the adhesive matrix or bindercomprising a polysilazane polymer and a polysiloxane polymer; andallowing said target compound to be adsorbed to particles of saidadsorbent material.

Other objects and features will be in part apparent and in part pointedout hereafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic longitudinal section of a pipette having afluid-permeable mass in the form of an adsorptive bed for use in apipette tip.

FIG. 2 is a schematic end view of a pipette having a fluid-permeablemass in the form of an adsorptive bed for use in a pipette tip.

FIG. 3 is a photograph showing morphology of a pipette tip having afluid-permeable mass in the form of an adsorptive bed before use.

FIG. 4 is a photograph as described in FIG. 3 after use.

FIG. 5 is a graph depicting flow and recovery data for Substance P, apeptide.

FIG. 6 is a graph depicting the cure time and temperature relationshipwith respect to selected peroxides (initiators) for conversion of thefluid polysilazane oligomer to the cross-linked polymer.

FIG. 7 is a graph depicting Thermal Gavimetric Analysis (TGA) used tomeasure the degree of conversion from the cross-linked polymer to theceramic material at elevated temperatures in different atmosphericconditions.

FIG. 8 compares the chromatographic analysis of a sample delivered to achromatographic column through a 316SS transfer line that has beentreated with polysilazane (FIG. 8A) vs. the analysis of an identicalsample that has been delivered to the column through an untreated 316SSline (FIG. 8B) as described in Example 14.

FIG. 9 is a depth profiling analysis for silicon, carbon, nitrogen,chromium, iron and oxygen using Energy Dispersive Spectroscopy (EDS) asdescribed in Example 16.

FIG. 10 depicts an infrared spectroscopy analysis of a silicon nitridepassivation coating as described in Example 15.

FIG. 11 depicts a graph showing the differential pore volume vs. thepore width for uncoated and coated Carboxen-1006 (FIG. 11A) and a graphshowing the differential pore volume vs. the pore width for uncoated andcoated 300 Å silica (FIG. 11B), both as described in Example 18.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the invention, it has been discovered that anamorphous non-glassy ceramic composition with highly useful propertiescan be prepared by curing, calcining and/or pyrolyzing the polysilazanepolymer. The composition obtained has been found to be not irreversiblyadsorptive for components of fluids that may come in contact with it. Ithas, therefore, been found useful as a passivating coating or film foran underlying substrate where it functions as a barrier againstadsorption of components of the fluid to the underlying surface of thesubstrate. Thus, the composition is useful as a coating for the walls ofa vessel containing the fluid, or for the interior wall of a conduitthrough which the fluid flows. The ceramic composition comprises anelement selected from the group consisting of silicon, a Group IIImetal, a Group IVA metal, a Group IVB metal, and combinations thereof.Preferably, the ceramic composition has a relatively low Young'smodulus, a relatively low flexural modulus, and a relatively highelongation as compared to crystalline silica or conventional silicaglass. Consequently, the composition possesses a greater degree offlexibility as compared to crystalline silica and conventional silicaglass. These properties are believed to contribute to the effectivenessof the ceramic composition as a barrier against adsorption of an analyteonto the underlying surface. The relatively greater flexibility of theceramic composition of the invention tends to reduce crazing andfracturing which might otherwise create fissures through which ananalyte could pass and be adsorbed to the substrate surface. The ceramiccomposition is characterized by a generally higher Young's modulus,higher flexural modulus and lower elongation than the polysilazanepolymer from which it is derived; but it retains properties effective toprotect its integrity against mechanical and thermal stresses to whichit and its underlying substrate may be subjected during service.

It has further been discovered that the amorphous non-glassy ceramiccomposition functions as a highly useful matrix for a particulateadsorptive material, and/or as a film for adhering such adsorptivematerial to an underlying surface. In this capacity, it again functionsas a barrier against adsorption to the substrate of a component of afluid in contact with the matrix or film. Thus, where the particulateadsorptive material is used in an adsorptive structure for the selectiveadsorption of an analyte from a fluid sample, such as a solid phaseextraction or microextraction device, or an open chromatographic column,the ceramic adhesive film or matrix allows the particulate adsorptivematerial to have access to the analyte, but prevents adsorption to thesubstrate that would otherwise compromise the selectivity of theadsorption process.

Further, in accordance with the invention, an adsorptive structure maycomprise a coherent body in which the aforesaid amorphous ceramiccomposition comprises a matrix wherein a particulate adsorptive materialmay be lodged. Discrete coherent bodies of this nature can serve, forexample, as packing for a chromatographic column.

The ceramic composition has a chemical structure comprising a network ofoxygen and silicon, Group III, Group IVA, or Group IVB atoms linkedpredominantly oxygen to silicon, Group III, Group IVA, or Group IVB atombonds. Without being held to any particular theory, it is believed thatGroup III metals and other Group IVA or Group IVB metals form bonds withnitrogen atoms in a manner similar to that of silicon atoms. Inparticular, germanium exhibits characteristics similar to that ofsilicon. The metals have an oxidation state of 3 or 4 and includegermanium, boron, aluminum, titanium and gallium. It is believed thatthe amorphous ceramic composition has a general structure comparable tosilicon oxide or germanium oxide, but differs in structure from silicaglass in a manner that contributes to its unique and advantageousproperties as a passivating film or matrix. Preferably, the ceramiccomposition comprises germanium or silicon, with silicon being economicand advantageous for an especially wide variety of applications.

In various preferred embodiments, the chemical structure of the ceramiccomposition may be interrupted either regularly or randomly by Group IVAor Group IVB atom to nitrogen atom or carbon atom linkages. Based onsputter depth profiling using Energy Dispersive Spectroscopy (FIG. 9),carbon and nitrogen atoms are present in the ceramic composition. Forexample, the ceramic composition may contain at least 30% carbon atomsand at least 2% nitrogen atoms at a depth of between about 1 and about2000 Å, more typically, at least 40% carbon atoms at a depth of betweenabout 1 and about 2000 Å, and/or at least 3% nitrogen atoms at a depthbetween about 1 and 2000 Å. Without being held to any particular theory,it is believed that these residual carbon and nitrogen atoms impart adegree of flexibility to the ceramic composition as compared tocrystalline silica and conventional silica glass. The exact mechanismfor imparting such flexibility is unclear. The flexibility of thecomposition may also, in part, be attributed to occlusions, perhaps veryfine occlusions, within the ceramic composition. It is theorized thatthese occlusions may cause weakness in the composition of a nature thatimparts a tendency to stretch or flex which exceeds any tendency tocrack or craze. Accordingly, the ceramic composition's flexibility maybe related to the residual carbon and nitrogen atoms and/or anyocclusions present.

The ceramic composition of the present invention is derived from anoligomer comprising repeating units in which nitrogen is combined withan element selected from the group consisting of silicon, a Group IIImetal, a Group IVA metal, a Group IVB metal, and combinations thereof.To form the ceramic composition, the oligomer and particulate adsorbentmaterial are heated. The characteristics of the ceramic composition areinfluenced by both the temperature and length of exposure to which theprecursor oligomer and particulate adsorbent material are subjected.When heated to an effective temperature range, the oligomer is convertedto a cross-linked polymer film. Typically, the cross-linked polymer filmmay be formed in a temperature range of between about 25° C. to about450° C. Upon heating to elevated temperatures, the cross-linked polymerfilm converts to a ceramic state. Typically, the conversion of thecross-linked polymer to the ceramic state occurs anywhere from about400° C. to about 2200° C. In one embodiment, the conversion of thecross-linked polymer film to the ceramic state occurs at greater thanabout 400° C.

The atmospheric conditions under which the heating occurs effects thenature of the cross-linking film that is formed. While the cross-linkedpolymer typically forms at a temperature of about 25° C. to about 250°C. in both air and inert atmospheres, the particular atmosphere doesinfluence the degree of mass conversion to the ceramic material. Thermalgravimetric analysis (TGA) may be used to measure this degree ofconversion. FIG. 7 shows the decline in weight of a polysilazane coatingas it is converted to an amorphous non-glassy ceramic film. The figureplots residual film weight as a function of temperature during thecuring process, expressed as a percentage of the initial dry polymerfilm weight. In air, approximately 95% of the weight of the startingmaterial is retained after the conversion to the ceramic state. Incontrast, in a nitrogen atmosphere, only about 75% of the weight of thestarting material is retained after the conversion to the ceramic state.Preferably, the conversion occurs in air.

The formation of the cross-linked polymer film at relatively lowtemperatures advantageously allows the film to be handled andmanipulated without any or with only minimal damage to the film. Also,the lower temperatures allow for easier application of multiplecoatings. Further, the conversion of the cross-linked polymer film tothe ceramic state at relatively low temperatures allows for a broaderrange of substrates to be utilized. In particular, certain substratesthat are susceptible to cracking or other types of degradation at hightemperatures, and thus unsuitable for coating, may be coated with theceramic film described herein at relatively lower temperatures.Additionally, because the conversion from the cross-linked polymer filmto the ceramic state may occur at temperatures lower than many otherapplications, common inexpensive ovens may be used to carry out theconversion, instead of relatively expensive high-temperature ovens.

The adsorptive structure of the present invention comprises betweenabout 0.1 and about 99.8% by weight particulate adsorbent material. Thepercentage by weight of particulate adsorbent material varies with theparticular application of the adsorptive structure. For example, whenused in chromatographic applications, the range is typically 1 to 83% byweight adsorptive material. Preferably, the adsorptive coating comprisesbetween about 20 and about 33% by weight adsorptive material.

The particulate adsorbent material may be nucleophilic, electrophilic,or neutral. For example, the particulate adsorptive material may beselected from carbon, organic polymers, silicas, zeolites, aluminas,metal or ceramic powders. Preferred organic polymer adsorbents useful inthe compositions and constructions of the present invention includepoly(divinylbenzene), copolymers or styrene and divinylbenzene, such asthat comprised by the porous nonionic polymeric adsorbent material soldunder the trade designation XAD™ by Supelco, Inc. of Bellefonte, Pa.,polystyrene, the porous highly cross-linked methacrylate copolymerresins comprised by the adsorbent material sold under the tradedesignation Amberchrom™, also by Supelco, acrylic ester copolymers,acrylonitrile-divinylbenzene copolymers and various polymers comprisingan aromatic backbone or aromatic pendant groups. A variety of othercross-linked polymer materials may also be used.

Carbon adsorbent material that are useful in practice of the inventioninclude Carboxen 1006™ and Carbopack Z™, both by Supelco, Inc.

Although porous adsorbent materials are preferred for many applications,the particulate adsorbent material of the invention may also beconstituted of substantially nonporous carbon, organic polymer or othernucleophilic materials.

Generally, the particulate adsorbent material range in size from about 1nanometer to about 1 millimeter. The particle size distribution of theparticulate adsorptive material is preferably such that at least 1% byweight thereof have a particle size from about 1 nanometer to about 1millimeter. Advantageously, at least about 50% by weight of theadsorbent material have a particle size from about 1 nanometer to about10 nanometers. For some applications, the particle size distribution ofthe particulate adsorptive material is such that at least 1% by weightthereof have a particle size from about 0.1 micron to about 10 microns.

Preferably, the particulate adsorbent material may have a B.E.T. surfacearea between about 0.1 and about 4000 m²/g. In certain preferredembodiments, the particulate adsorbent material has a B.E.T. surfacearea of at least 100 m²/g. For certain other applications, e.g., use asan adsorbent bed in pipette tips, the particulate adsorbent materialpreferably has a B.E.T. surface area of at least 1 m²/g and preferablyat least 35 m²/g. Typically, the adsorptive material may have a porevolume of about 0.01 to about 5 cc/g. For many embodiments, at least 85%of the pore volume of the particulate adsorptive material is constitutedof pores having a pore size between about 2.5 Å and about 10,000 Å. Forcertain applications, at least 75% of the pore volume of the adsorptivematerial is constituted of pores having a pore size between about 3 toabout 20 Å. For certain other applications, at least 75% of the porevolume of the adsorptive material is constituted of pores having a poresize between about 100 to about 300 Å. For still other applications, atleast 75% of the pore volume of the adsorptive material is constitutedof pores having a pore size between about 100 to about 2000 Å. In aparticularly preferred embodiment, the adsorbent material is carbonbased having a particle size predominantly between 0.2 and about 2.0 μm,a total pore volume of between 0.1 and about 3 cc/g, a macropore(diameter>500 Å) volume of between about 0.1 and about 2.0 cc/gm, amesopore (diameter between 20 and 500 Å) of between about 0.1 and 2.0cc/g, and a micropore (diameter 3 to 20 Å) of between about 0.1 andabout 2.0 cc/g. Graphitic carbons are generally non-porous and presentan external surface area in the range of 1 to 100 m²/g. These may besuitable. A useful graphitized carbon sold by Supelco under thedesignation Carbopack X has a B.E.T. surface area of about 250 m²/g andcomprises a modest level of microporosity, less than about 0.5 cc/g.

Adsorbent material consisting of zeolite molecular sieves typically havea particle size of between 0.1 and about 5 microns, an average porevolume in the range of between about 0.3 and about 0.7 cc/g, and anaverage pore size in the range of about 5 Å. The B.E.T. surface area ofzeolite molecular sieves is generally in the range of about 250 to about400 m²/g.

Adsorbent material consisting of activated alumina are generally in thesubmicron particle size range, i.e., between about 0.1 and about 5microns. Activated alumina has an average pore size in the range ofabout 2 to about 100,000 Å, a pore volume of between about 0.25 andabout 1 cc/g, and a B.E.T. surface area in the range of about 300 toabout 400 m²/g.

Activated silica adsorbent material have a particle size of betweenabout 1 and about 10 microns, an average pore size of between about 0and about 1000 Å, and a pore volume of between about 0.5 and about 20cc/g. Silica gel has average pore size in the range of between about 3and about 500 Å, and an average pore volume in the range of betweenabout 0.5 and about 20 cc/g, and is available in a typical particle sizeof between 1 and about 1,000. B.E.T. surface area is ordinarily in therange of between about 20 and about 400 m²/g in the case of activatedsilica, and between about 50 and about 1300 m²/g in the case of silicagel.

Porous organic polymers produced by emulsion and/or suspensionpolymerization may be nondisperse (with respect to particle size), i.e.,narrowly distributed within a particle size range of between about 1 andabout 2 microns. Such porous polymer bodies exhibit a very wide range ofB.E.T. surface areas, e.g., from about 1 to about 1300 m²/g, commonly500 to 900 m²/g, most typically 700 to 800 m²/g. Pore sizes are in therange of between about 100 and 200 Å. Pore volume is generally in therange of between about 0.2 and about 2 cc/g.

For purposes of this disclosure, specific surface area, total porevolume, pore size distribution and contribution to total pore volume arevalues determined using nitrogen porosimetry analysis such as thatdescribed by S. J. Gregg and K. S. W. Sing in Adsorption, Surface Areaand Porosity, Academic Press, New York, 1982 and P. A. Webb and C. Orrin Analytical Methods in Fine Particle Technology, Micromeritics,Norcross, Ga., 1987, the entire disclosures of which are incorporatedherein by reference. An ASAP 2010 porosimeter (micromeritics, Norcross,Ga., USA), a surface area and pore volume instrument, was used toacquire the data reported herein in Example 18 and FIGS. 11A and 11B.Specific surface area determination involves exposing a known weight ofa solid to some definite pressure of a non-specific adsorbate gas (i.e.,nitrogen) at a constant temperature, e.g., at the temperature of liquidnitrogen, −196° C. During equilibration, gas molecules leave the bulkgas to adsorb onto the surface of the solid which causes the averagenumber of molecules in the bulk gas to decrease which, in turn,decreases the pressure. The relative pressure at equilibrium (p) as afraction of the saturation pressure (p₀) of the adsorbate gas isrecorded. By combining this decrease in pressure with the volumes of thevessel and of the solid sample, the amount (i.e., the number ofmolecules) of gas adsorbed is calculated by application of the ideal gaslaws. These data were measured at relative pressures (p/p₀) ofapproximately 0.001 to 0.05 where the Brunauer-Emmett-Teller (BET)equation for multi-layer adsorption typically applies. With the numberof adsorbed gas molecules known, specific surface area was calculatedusing the known cross-sectional area of the adsorbate gas, nitrogen. Forcases where only physical adsorption due to Van der Waals forces occurs(i.e., Type I Langmuir isotherms), the determination of surface from theobserved changes in pressure is accomplished using the BET equation.Pore size and pore size distributions were calculated by obtainingrelative data approaching p/p₀=1, i.e., in the regime where multi-layeradsorption and capillary condensation occur. By applying the Kelvinequation and methods developed by Barrett, Joyner and Halenda (BJH), thetotal pore volume and contribution to the total pore volume wereobtained.

The Density Functional Theory (DFT) plots, shown in FIGS. 11A and 11B,are graphs of the relative pressure values, p/p₀, which are correlatedto the respective pore diameters, using a series of mathematicalequations, at which the relative pressure values are obtained. Theresulting plot thus relates the pore diameter, in angstroms, to the porevolume (i.e., the quantity of nitrogen adsorbed in the specified porediameter region) values obtained.

With respect to FIG. 11A, the porosimetry data obtained indicates thatthe surface area was slightly reduced, but a significant amount ofmicropore region remained (site of primary adsorption work). Also, themesopore and macropore diameters did not significantly change, as seenin the DFT plots. With respect to FIG. 11B, the data obtained indicatesthat a small amount of microporosity was created by the 2 adhesiveslaying in the pores, and a small amount of mesoporosity was lost due tothe presence of the adhesives. However, a significant amount of workingpore remained to perform the adsorption work.

The amorphous non-glassy ceramic composition may be applied to anunderlying surface consisting of glass, or a non-glass material such as,for example, metal, plastic, wood, fabric, ceramic or combinations ofthereof. For a wide variety of applications, the underlying surface ismetal or glass. Preferable metals include, for example, copper,aluminum, steel, stainless steel, nitinol, bronze, zirconium, titanium,and nickel. The surface may be of any geometry capable of being coatedby any known conventional method. In particular, surfaces may includetubing, transfer lines or other conduits, the interior wall of thebarrel of a syringe (such as that used for sample transfer or for anSPME device as described in Pawliszyn U.S. Pat. No. 5,691,206), theinterior surface of a thermal or solution desorption device,chromatographic fittings (such as valves, tees, elbows and the like),diaphragms, rotors, pathways, a vessel for conducting reaction oradsorption operations, the surface of an agitator for a stirred reactionvessel or adsorption contactor, GC and LC columns and instrumenthardware (such as injection material liners, inlet disks, wool, detectorassemblies, e.g., FID jets, mass spectrometry assemblies, e.g., ion trapparts), HPLC column hardware, sample loops, frits, filling devices forcorrosive solid phase extraction materials, general housing andassemblies (such as nozzles, combustion/reaction chambers, spray rings,flow restrictors and the like), MALDI sampling plates, surfaces thatrequire changes in hydrophobicity or chemical wettability, andcontainers for liquids and gases including SUMMA or TO type sampling. Ina preferred embodiment, the underlying surface of the adsorptivematerial is an interior wall of a conduit or vessel for storage ortransport of a fluid therein.

Generally, the ceramic composition has a thickness between about 1nanometer and about 1 millimeter. Multiple layers of the ceramiccomposition may be provided over a substrate surface. By applying morethan a single layer, cracking of the ceramic composition may bedecreased or eliminated.

The ceramic composition may also comprise filler material to increasethe thickness of the ceramic coating. Increasing the thickness of thecoating may advantageously increase the physical strength of thecoating, increase abrasion resistance, and provide increased protectionof the underlying substrate. Filler material includes carbon, metalpowders, ceramic powders, graphite, flakes, mica, zirconium and fumedsilica. In a preferred embodiment, the filler material is mica, fumedsilica, or zirconium. The filler material selected should benon-adsorptive for an analyte and preferably non-adsorptive for allcomponents of a fluid which comes into contact with the ceramiccomposition.

To bond the particulate adsorbent material to the substrate, theparticles are preferably suspended in a solution of the silazaneoligomer or polymer and the substrate is contacted with the suspensionat a temperature in the aforesaid range. The suspension may be preparedeither with or without the aid of a solvent. When a solvent is used,essentially any organic solvent that provides effective solubilizationof the polysilazane polymers and wets the particulate adsorbent materialcan be used for the reaction. Among the organic solvents that mayconveniently be used are alcohols such a methanol, ethanol, isopropanol,and n-butanol, ketones such as methyl ethyl ketone, methyl isobutylketone, and methyl isopropyl ketone, ethers such as diethyl ether,methyl ethyl ether, and dipropyl ether, esters such as ethyl acetate,methyl butyrate, or amyl acetate, aromatic solvents such as benzene,toluene, and xylene, halogenated solvents such as chloroform,trichloroethane, and dichloromethane, and other common solvents such asdimethylformamide, dimethyl sulfoxide, tetrahydrofuran, etc. Aproticsolvents such as carbon disulfide and acetonitrile are also useful.Preferably, the solvent used is effective to wet the particulateadsorptive material, preferably carbon particles, at a temperature up toabout 1000° C. Preferred solvents for this embodiment of the inventioninclude pentane and dichloromethane. For graphitic carbon,tetrahydrofuran is especially preferred.

It is desirable to maintain the reaction mixture substantially free ofmoisture. As the most common source of moisture, the solvent preferablyhas a moisture content not greater than about 50 ppm, more preferablynot greater than about 10 ppm. Conveniently, the polysilazane polymer isdissolved or dispersed in the solvent with aid of agitation or exposureto ultrasound. Mechanical agitation or sonication are also preferablyused to aid in obtaining a uniform dispersion of the adsorptive materialin the solution.

Concentrations and ratios of reactants are not narrowly critical; nor ispressure. Conveniently, the silazane content of the solution ordispersion may be between about 1 and about 1000 gpl, and theconcentration of carbon or other dispersed particulate adsorptivematerial in the pre-reaction slurry may be in the range of between about1 and about 500 gpl, ordinarily 10 to 100 gpl. The ratio of the silazaneto adsorbent is preferably from about 20 to 1 to about 1 to 1, morepreferably from about 10 to 1 to about 2 to 1, and even more preferablyfrom about 5 to 1 to about 2 to 1. More concentrated coating solutions,in the range of 35 to 80 gpl can be used to provide multiple layers ofcarbon in a single coat. Concentrations in the 10 to 30 gpl aregenerally effective to provide only a single layer of carbon particlesof typical size, e.g., 0.2 to 1 micron. Nevertheless, coatings havingmultiple layers of carbon particles can be obtained from such relativedilute compositions by applying the coating in multiple cycles.

The reactions are readily conducted at ambient pressure, but pressuresranging from a high vacuum, −29.90″ Hg, to a positive pressure of up to10,000 psi can be tolerated without adverse effect on the reaction. Whenthe slurry of particulate adsorptive material, generally carbonparticles, in silazane solution has been brought into contact with thesubstrate, the solvent is removed. Preferably, the solvent is removed byevaporation, although other means known in the art may be utilized, suchas, for example, sublimation.

The particulate material may be lodged in a matrix comprising theceramic composition and/or adhered to an underlying substrate via a filmcomprising the ceramic composition. Where the adsorptive material islodged in a ceramic matrix, particles of the adsorptive material may beaccessible to an analyte by outcropping from the matrix or by flow ofanalyte through pores in the matrix to the adsorbent.

Further, the ceramic composition may be formed as a coherent body. Thecoherent body may comprise a core mass which may be coated with theceramic composition. In such instance, the core mass may be selectedfrom metal, glass, carbon, and silica. A preferred core mass is silica.An adsorptive structure may comprise a coherent body in whichparticulate adsorptive material is lodged in a matrix comprising theceramic material. As discussed above, the particulate material mayoutcrop from the ceramic matrix; or an analyte in a fluid with which thecoherent body is contacted may have access to the adsorptive particlesby flow through pores in the matrix. An adsorptive bed may be formedfrom a plurality of discrete adsorptive bodies having any of thealternative structures described above. Such adsorptive bed mayfunction, for example, as packing for a chromatographic column. Such acolumn may comprise a tubular member containing a bed comprising suchpacking material. The adsorptive structure may also comprise amonolithic mass consisting essentially of the ceramic composition.

In any of the various embodiments detailed above, the ceramic film, inwhich the particulate adsorptive material is lodged, may notsubstantially be irreversibly adsorptive of an analyte or other targetcompound that is adsorbed by said particulate adsorptive material. Inthis manner, the analyte is adsorbed almost entirely by the particulateadsorptive material thereby increasing the selectivity of adsorption.

The exact chemical nature of the ceramic composition has not beendetermined. However, using data from infrared spectroscopy and EDS depthprofiling analysis, certain assumptions and characterizations may bemade. For example, using EDS depth profiling analysis (see FIG. 9) at adepth of about 1 to about 2000 Å, carbon atoms have been found to bepresent in an exemplary ceramic composition at a concentration of atleast 40%. Further, at the same depth range in the same example,nitrogen atoms have been found to be present at a concentration of atleast 4% and Si—O bonded atoms have been found to be present at aconcentration of at least 10%.

The information garnered from the Energy Dispersive Spectroscopy depthprofiling analysis may be combined with information from IR spectroscopyto further characterize exemplary ceramic compositions. FIG. 10 depictsan IR spectra showing the composition of a polysilazane precursormaterial versus the composition of a ceramic film obtained by curing theprecursor at 200° C. for 10 minutes, then 450° for 10 minutes. Theprecursor material possesses a characteristic band at 3384 cm⁻¹representing Si—NH—Si bonds. This band is almost nonexistent in thefinal ceramic composition, indicating that such bonds are no longerpresent. Similarly, the Si—H band at 2136 cm−1 of the precursorpolysilazane film is not present in the final ceramic composition.However, the C—H band in the polysilazane film remains in the ceramiccomposition, although at a lesser intensity. These findings areconsistent with findings of other researchers. D. Bahloul, et al. foundthat when pyrolysis temperature is increased, a decrease in theintensity is observed as well as a broadening of adsorption bands in asample of the general formula (SiViH—NH)_(n) where “Vi” is a vinylgroup. Djamila Bahloul, et al., Pyrolysis Chemistry of PolysilazanePrecursors to Silicon Carbonitrile, J. Mater. Chem., 1997, 7(1), pp.109-116. In particular, the spectrum of a sample polysilazane pyrolyzedat 250° C. indicated a decrease in the band intensities of vinyl groupsat 3047, 1592, and 1406 cm⁻¹. The Si—H stretching band at 2135 cm⁻¹ wasalso less modified. At 500° C., the adsorption bands arising from theN—H (3400, 1170 cm⁻¹), Si—H (2130 cm⁻¹) and vinyl groups (3050, 1594,1404 cm⁻¹) were reduced considerably. As the temperature increased, theresidual Si—H, N—H, and C—H bonds were eliminated.

An exemplary ceramic composition found to be useful in the variousadsorptive structures and other embodiments of the invention has beenfound to exhibit an infrared vibrational absorption spectrum having acharacteristic band of about 2976 cm⁻¹ for C—H. Additionally, thisexemplary ceramic composition was found to have an infrared vibrationalabsorption spectrum having the following series of characteristic bandranges (values are in cm⁻¹): from about 1200 to about 900 for Si—O; fromabout 900 to about 600 for Si₃N₄; and from about 900 to about 600 forSi—C. Preferably, the ceramic composition may have an infraredvibrational absorption spectrum comprising the following series ofcharacteristic band ranges at 250° C. (values are in cm⁻¹): about 3047,1592, and 1406 for vinyl groups; and about 2135 for Si—H (stretching);and the following series of characteristic band ranges at 500° C.(values are in cm⁻¹): about 3400 and 1170 for N—H; about 2130 for Si—H;and about 3050, 1594, and 1404 for vinyl groups. Generally, the ceramiccomposition as measured by infrared spectroscopy may exhibit a decreasein the intensity of vinyl groups at 250° C. relative to said intensityat ambient temperature. Further, the ceramic composition may exhibit adecrease in the adsorption bands of vinyl and N—H groups at 500° C.relative to said adsorption bands at 250° C.

As previously noted, the ceramic composition of the present inventionmay be derived from an oligomer comprising repeating units in whichnitrogen is combined with an element selected from the group consistingof silicon, a Group III metal, a Group IVA metal, a Group IVB metal, andcombinations thereof. The oligomer may be combined with the particulateadsorptive material and heated to an effective temperature, as discussedherein, to first form a cross-linked polymeric film. Upon heating to amore elevated effective temperature, the cross-linked polymer film isconverted to the ceramic composition. The temperatures for conversion tothe polymer film and ceramic composition are as previously discussed.The conversion of the oligomer to the polymeric matrix or film andsubsequent conversion to the ceramic composition may occur in air or inan inert atmosphere.

In a preferred embodiment, the silazane oligomer comprises repeatingunits having the formula:

wherein:

R₁ is selected from the group consisting of hydrogen, vinyl, alkyl,hydroxy, alkoxy, amino, alkylamino, mercapto, acetoxy, halo,hydroxyalkyl, dimethylamino, oxime, isocyanate, CH₂Q-(OCH₂CH₂)_(n)OH,

R₂ is selected from the group consisting of methacryl, C₁₋₂₀ alkyl,C₂₋₂₀ alkenyl, fluoroalkyl, carbonyl, carbinol, glycidyl, straight,branched or cyclic —(CH₂—O—CH₂)_(n), and aryl optionally substitutedwith C₁₋₆ alkyl, fluoro, chloro, cyano or aryl;

Q is C₁₋₈ alkyl; and

n is 1 to about 20.

Preferably, R₁ is selected from the group consisting of hydrogen, vinyl,alkoxy, hydroxy, and alkyl. More preferably, R₁ is a vinyl group in atleast one of the repeating units.

Preferably, R₂ is selected from the group consisting of hydrogen, vinyl,alkyl, aryl and fluoroalkyl. More preferably, R₂ is hydrogen or methyl.

In any of the above embodiments, n is preferably 2 to about 12, morepreferably 3 to about 8, and most preferably 3 to about 6.

Advantageously, the oligomer comprises a cyclic silazane having fromabout 6 to about 10 ring atoms and having at least one vinylsubstituent. In one particularly preferred embodiment, the oligomer hasthe formula:

wherein R is H or —CH═CH₂ and n is 1 to 20.

The method of preparation of cyclic silazanes in accordance with thepresent invention can be found in U.S. Pat. No. 6,329,487, which ishereby incorporated in full by this reference. As described by U.S. Pat.No. 6,329,487, cyclic silazanes may be prepared from starting compoundssuch as methyldichlorosilane. During the initial ammonolysis, thesilicon-chlorine bonds undergo ammonolysis thereby generating adiaminosilane, which is further converted into a linear moleculecontaining several Si—N structural units. This reaction is shown below.

The linear structure is stabilized in anhydrous liquid ammoniacontaining an ionized ammonium halide salt dissolved therein. Thisionized and dissolved ammonium halide salt acts as an acid catalystwhich catalyzes a loss of Si—H bond to generate a new silicon-chlorinebond on the straight chain of the polymer. It is theorized that thislinear structure can cyclicize forming a small ring in contact with theanhydrous ammonia solution as shown below.

Generally, the silazanes and polysilazanes of the present invention canbe prepared by the methods described in U.S. Pat. No. 6,329,487.Specifically, at least one halosilane, preferably having at least oneSi—H bond, is introduced into at least twice the stoichiometric amountof liquid anhydrous ammonia relative to the silicon-halide bonds, andpreferably at least from about five to about ten times. The anhydrousammonia is maintained at a sufficient temperature and/or pressure toremain liquified during the process. During the ammonolysis process,ammonium halide salt created as a co-product is retained in theanhydrous liquid ammonia solution. The ammonium halide salt issubstantially ionized and solubulized in the anhydrous liquid ammonia,and as such, provides an acidic environment for catalytically preparingthe silazane and polysilazane compounds useful for the presentinvention.

In one preparation of an adsorptive structure, a flowable dispersion maybe prepared comprising the oligomer and the particulate adsorbentmaterial. The dispersion may then be applied to a surface of a substrateand heated to an effective temperature to form the ceramic composition.The dispersion may be applied by any known means of application. Inparticular, the dispersion may be applied by spray, brush, spin or dipcoating or any combination thereof. Further, static or dynamic coatingmethods may be used in applying a coating comprising single or multiplelayers. In the static method, a slurry of particulate adsorptivematerial, preferably carbon particles, in a silazane polymer solution isapplied as a wet coating to the surface of the substrate, and solventremoved by application of heat and/or vacuum. Depending on theconcentration of the carbon particles and the viscosity of the solution,a coating of 1 to about 20 carbon particles in thickness may be obtainedin a single coating cycle. According to the dynamic coating method, theslurry is forced from a reservoir through a tubular column that is to becoated under inert gas pressure. A slug of the slurry moves ahead of thegas phase, leaving behind a film adhering to the interior column wall.As the slug moves forward, an annular transition segment of the slurry,having roughly a conical inside surface, moves along the wall behind theslug intermediate the slug and the wet, stable cylindrical film that isdeposited on the wall. The thickness of the stable film is a function ofthe angle between the wall and the interior conical surface of thistransition segment. It has been found that thicker films are associatedwith both high carbon concentration in the slurry and a relatively steepangle between the slug and substrate, i.e., both the advancing angle atwhich the front face of the slug meets the substrate, and the trailingangle between the transition segment and the substrate; and further thatthe steepness of the angle varies directly with the gas pressure.

In another preparation, the ceramic matrix composition is formed fromheating a coherent precursor mass comprising the oligomer. The precursormass may be formed from a dispersion comprising the particulateadsorptive material and the oligomer. Upon heating, the precursor massproduces a coherent body comprising the particulate adsorptive materialdispersed in a matrix comprising the ceramic composition. Alternatively,the adsorptive particulate material may be applied over the surface ofthe coherent precursor mass comprising the oligomer. The resultantcombination of the oligomer and the particulate adsorptive material maythereafter be heated to form a coherent body comprising the structurewherein the ceramic composition having the adsorptive material isdispersed over the ceramic composition surface.

Adsorptive coatings and structures generally of the type describedhereinabove may be utilized in a chromatographic separation method.According to such separation method, a mobile fluid phase containing ananalyte is contacted with a stationary phase comprising particulateadsorptive material that is lodged in a matrix comprising an amorphousnon-glassy ceramic composition and/or adhered to an underlying surfacevia a film comprising an amorphous non-glassy ceramic composition. Theceramic composition comprising an element selected from the groupconsisting of silicon, a Group III metal, a Group IVA metal, a Group IVBmetal, and combinations thereof. The nature of the ceramic compositionis the same as described above. The stationary phase of this embodimentmay be comprised of a packing for a chromatographic column or solidphase extraction device. The packing may be comprised of discreteadsorptive bodies as discussed herein having particulate adsorptivematerial lodged in a matrix of ceramic composition. Alternatively, thestationary phase comprises a ceramic film on the interior surface of achromatographic column with the particulate adsorptive material beinglodged in the film and/or adhered to the interior surface via the film.Preferably, the ceramic composition is not irreversibly adsorptive of ananalyte contained in the mobile phase, more preferably not irreversiblyadsorptive of any component of the mobile phase other than a carrierfluid. Most preferably, the ceramic composition is also not irreversiblyadsorptive of the carrier fluid.

The present invention contemplates chromatographic methods including GC,liquid chromatography, PLOT, SPE, Maldi, TLC, and SPME. Depending on thetype of chromatography being performed, the form of the ceramiccomposition may vary. For example, the ceramic composition may be in theform of a film or adsorptive bed, as previously described. For example,if high molecular weight analytes are to be chromatographicallyseparated, then a thin film is preferred to minimize strong adsorptionof the analytes to the film or low surface area adsorptive bed. If lowmolecular weight/low boiling point analytes are to be analyzed, then anadsorptive bed comprised of high surface area porous solids is preferredto effectively separate the analytes.

In another embodiment of the present invention, a chromatographicseparation device comprising a tubular column and, on a wall of saidcolumn, a coating is contemplated. The coating is a film comprising anamorphous non-glassy ceramic composition and a particulate adsorptivematerial. The adsorptive material is lodged in the film and/or adheredvia the film to the wall. The ceramic composition comprises an elementselected from the group consisting of silicon, a Group III metal, aGroup IVA metal, a Group IVB metal, and combinations thereof.

In the above described vessels, conduits, devices and other embodiments,the amorphous non-glassy ceramic composition may be applied to asubstrate providing a barrier against adsorption onto the surface of acomponent in a fluid stored in the vessel or transported via the conduitor device. The ceramic composition is derived from an oligomercomprising repeating units in which nitrogen is combined with an elementselected from the group consisting of silicon, a Group III metal, aGroup IVA metal, a Group IVB metal, and combinations thereof. Thecoating, such as, for example, a film or thin layer, is effective topassivate a surface of a substrate where the function is mainly topassivate and prevent loss of an analyte to the walls of a vessel orconduit, the coating contains no particulate adsorbent material. Thecoating may be prepared by applying to the surface of the substrate asolution or flowable dispersion comprising the oligomer and heating thesolution or dispersion to form the ceramic composition. As with theother embodiments, the oligomer may be heated to a temperature effectiveto convert it to a cross-linked polymer film. This cross-linked polymerfilm may be further heated at a more elevated temperature to convert itto a ceramic state. The temperature ranges for both conversions are aspreviously described.

By applying the passivation coating to a surface of a substrate, asdescribed above, the coated surface becomes non-adsorbent for an analytecontained in a fluid having contact therewith. As a result, less analyteis lost to interactions with the substrate. In particular, for SPMEapplications, in which a very minute amount of analyte is adsorbed, lossof even a fraction of the analyte to interactions with an uncoatedsurface may affect analytical results. Although SPME is an importantapplication of the technology described herein, it is not so limited.FIGS. 8 a and 8 b, for example, show gas chromatographic (GC) analysisof trace levels of water and carbon disulfide. In the process whichyielded the chromatogram of FIG. 8 a, the sample has been fed through astainless steel transfer line treated with a polysilazane passivationcoating. In the process which produced the chromatogram of FIG. 8 b, thestainless steel transfer line is untreated. From a comparison of thegraphs, it is evident that the polysilazane treated tubing is adequatelyinert for active compound transfer into the analytical column resultingin separation and detection of the water and carbon disulfide analytes.

In one class of embodiments wherein the coating is used for passivationof a surface, the underlying surface is substantially glass, theunderlying surface comprising of, for example, inlet sleeves, wool,syringe barrels, sample vials, connectors (such as press-tight, column,and seal), adsorbent trap assemblies and thermal tubes.

In a preferred class of embodiments wherein the coating is used forpassivation of a surface, the underlying substrate is substantiallynon-glass. The non-glass substrate may be selected from the groupconsisting of metal, plastic, wood, fiber, fabric, ceramic orcombinations thereof. A preferred non-glass substrate is metal.Alternatively, the non-glass substrate may be selected from copper,aluminum, steel, stainless steel, nitinol, bronze, zirconium, titanium,and nickel. The coating may be applied to any shape of surface. Inparticular, the coating may be applied to a non-glass conduit or vessel.

In those embodiments wherein the coating is used for passivating asurface, the substrate to be coated includes the interior walls or otherworking surfaces of devices and fittings which may come in contact witha fluid containing an analyte. Such devices and fittings may includetubing, transfer lines, pipe, valves, fittings and regulators (such asfrits, diaphragms, rotors, pathways), GC and LC column and instrumenthardware (such as GC injection materials liners, inlet disks, wool) GCdetector assemblies (such as FID jets, mass spectrometry assemblies suchas ion trap parts), HPLC column hardware, sample loops, and frits. Othersurfaces include filling devices for corrosive solid phase extractionmaterials, SPME assemblies, general housing and assemblies (such asnozzles, combustion/reaction chambers, spray rings, flow restrictors),MALDI sampling plates. Further surfaces that may be suitable for thepassivation coating include any surface that requires changes inhydrophobicity or chemical wettability, containers for liquids andgases, including SUMMA or TO type sampling canisters.

Optionally, the passivation coating functions to change thehydrophobicity/hydrophilicity of an underlying surface. In suchembodiments of the invention, the surface of the ceramic film isderivatized to alter the characteristics of the underlying surface. Inone application, the surface of a MALDI sample slide is converted to ahydrophobic surface so that when a water-based sample is applied to thesurface of the slide, the geometry is preserved. In particular, thesample beads up on the surface of the slide allowing for a moreconcentrated sample and improved laser analysis.

The invention is further directed to a fluid-permeable mass comprisingparticulate adsorbent material that may be dispersed in a matrixcomprising a polysilazane polymer and a polysiloxane polymer. Thefluid-permeable mass may have a permeability of about 5 to about 20μL/second. Preferably, the matrix is substantially not irreversiblyadsorptive of an analyte or other target compound that is adsorbed bythe particulate adsorbent material. Generally, the particulateadsorptive material may be selected from among those previouslydescribed. Advantageously, the fluid-permeable mass may contain at least40% by weight of the particulate adsorptive material. Preferably, thefluid-permeable mass contains between about 50 and about 75% be weightparticulate adsorptive material. The B.E.T. surface area of theparticulate adsorbent material may be at least 1 m²/g, preferably atleast about 35 m²/g. Further, the concentration of the particulateadsorptive material may be such that the surface area thereof is atleast about 0.1 m²/cc of the fluid-permeable mass. Still further, theadsorptive material may have a pore volume of about 0.01 to about 5cc/g. Typically, at least 85% of the pore volume of the particulateadsorptive material is constituted of pores having a pore size betweenabout 2.5 Å about 10,000 Å. Preferably, for adsorption/desorption ofpeptides and proteins, a non-polar adsorbent with a pore size of about200-300 Å should be selected. The particular adsorptive material isdetermined by the nature of the analyte sought. For a large number ofapplications a C₁₈-derivatized silica is preferred. One skilled in theart can readily determine an appropriate particulate adsorbent material.

The combination of the polysilazane polymer and the polysiloxane polymerof the present embodiment has particularly good qualities in thepreparation of pipette tips wherein the fluid-permeable mass is in thetip of the pipette. The pipette tip can be constituted of any suitablematerial such as, for example, polyolefins, acrylates, methacrylates,stainless steel or Teflon. A preferred material is polypropylene. Thetip may or may not be tapered. However, tapering of the pipette tip mayprovide better drop formation leading to less loss of analyte. Further,the particular size of the pipette opening influences the dropformation. For example, a tip orifice from about 350 microns to about750 microns provides excellent drop formation of the final drop offluid, thereby decreasing any opportunity for loss of analyte.

The use of both a polysilazane and a polysiloxane polymer, as opposed tothe use of either one alone, provides superior adhesive properties. Theadvantageous adhesive qualities of the polysilazane and polysiloxanemixture allow for adhesion of the fluid-permeable mass (“an adsorbentbed”) to the walls of a pipette tip. As further discussed below, theadsorptive mass may be formed in the tip by introducing a dispersioncontaining the binder polymers and the particulate adsorbent in asolvent vehicle. Although a siloxane alone functions well as anadhesive, the cured polysiloxane is inadequately permeable to a fluidsample, and thus inhibits access of an analyte to the adsorbentparticles contained in the bed. If the siloxane concentration in thedispersion is reduced in an effort to impart porosity, there is atendency for the adhesive to break in the middle/interior section of thebed, in which case the fluid sample may channel through the bed ratherthan gaining access to the adsorbent particles. On the other hand,silazane alone functions well to maintain the integrity of themiddle/interior section of the adsorbent bed while maintaining effectivetip flow, but the adhesion of the bed to the pipette tip walls isineffective. Additionally, the use of a silazane adds stability to thesiloxane adhesive (i.e., eliminates swelling) and improves flow of thefluid containing the analyte through the bed. It is believed that theimproved flows result from slight constriction of the adhesivecombination which opens the interstitial space(s) of the adsorbent bed.Accordingly, the combination of a siloxane and silazane polymerfunctions to overcome these obstacles by providing an adhesive thatfunctions to (1) eliminate bed breakage in the middle/interior sectionof the bed thereby stabilizing the tip, (2) permit effective tip flow,(3) improve analyte recovery due to the inertness of the tips, (4)increase binding capacity since little or no adhesive interferenceoccurs with the adsorbent, and (5) improved adherence of the bed to thepipette tips walls due to the adhesive strength of the adhesivecombination.

The chemical structure of the silazane is as described previouslyherein. A preferred silazane is an oligomer or polymer having amolecular weight of about 200 to about 2,000,000, more preferably fromabout 200 to about 600.

The general chemical structure of the polysiloxane repeating units maybe represented by the following formula:

wherein

R₃ is hydrogen, substituted or unsubstituted hydrocarbyl, alkoxy,aryloxy, nitro, cyano, amino, hydroxy, or an —O—Si≡ moiety; and

R₄ is hydrogen, methacryl, C₁₋₂₀ alkyl, C₂₋₂₀ alkenyl, fluoroalkyl,carbonyl, carbinol, glycidyl, straight, branched or cyclic—(CH₂—O—CH₂)_(n), and aryl optionally substituted with C₁₋₆ alkyl,fluoro, chloro, cyano or aryl.

Preferably, one of R₃ and R₄ is hydrogen in about 1% to about 10% of thepolysiloxane repeating units, more preferably from about 3% to about 8%.

The siloxane may include polar groups such as, for example, —OH,—(CH₂)_(n)CN, —C₆H₅—OH, or —C₆H₅—NH₂. Generally, the polysiloxane tipfor use in certain pipette tip applications is a long-chain polymerpreferably with a molecular weight of about 400,000 to about 800,000. Atypically useful polysiloxane has a molecular weight of approximately600,000. The chain should be of sufficient length to wrap around theparticulate adsorbent material, i.e., C₁₈-silica, and also havesufficient surface contact to covalently bond with the polyolefin,acrylate, methacrylate, stainless steel or Teflon pipette tip walls andstabilize the entire adsorbent bed. A preferred siloxane ispolydimethylsiloxane with 1-10% Si—H groups (approximately 600,000 Mw).

U.S. Pat. No. 5,599,445, incorporated herein in its entirety, describesan improved means of bonding granular, particulate, or fibrousadsorptive material to a substrate. Generally, it disclosed that thedirect C—Si bond between an adsorptive carbon or polymer body and asiloxane polymer provides an advantageous means for bonding an adsorbentto a substrate, such as, for example, glass. Preferably, the siloxanehas the formula:

wherein

R is hydrogen, substituted or unsubstituted hydrocarbyl, alkoxy,aryloxy, nitro, cyano, amino, hydroxy, or an —O—Si≡ moiety;

R¹, R², R³, R⁴, R⁵, R⁶, R⁷, and R⁸ are independently selected from thegroup consisting of hydrogen, substituted or unsubstituted hydrocarbyl,nitro, cyano, and an —O—Si≡ moiety; and

m+n is such that the average molecular weight of the polymer is betweenabout 80,000 and about 2 million, preferably between about 250,000 andabout 500,000.

It is generally preferred that at least one of R¹ through R⁸ behydrogen, so that the polysiloxane has a hydrosilyl functionality of atleast 2. Having such a structure, the polymer can react with both carbonat the surface of the carbon adsorptive material, to provide thethermally stable ≡C—Si≡ bond, and silanol groups at the surface of theglass to provide the —Si—O—Si—bond through which the polysiloxane isbound to the glass. While a hydrosilyl functionality of 2 is the minimumrequired for the above reaction, it is generally preferred that betweenabout 1% and about 10% of the R¹ through R⁸ substituents on the backbonesilicon atoms be hydrogen.

Many suitable siloxane polymers are immiscible with polar solvents,while the silazane polymer is usually miscible with both polar andnon-polar solvents. The use of a non-polar siloxane with an apolarsilazane may advantageously force the analytes into the pores of theparticulate adsorbent material, i.e., C₁₈-silica, where theadsorption/desorption work is performed. Typically, the solvent assistsin the dispersion of the adhesive so it does not block the pores of theadsorptive particles. Without being held to any particular theory, it isbelieved that rapid evaporation of the solvent is the driving force thatpulls the siloxane away from the pores.

The selection of a solvent is largely based on density and miscibilitywith the siloxane. The solvent has a desired density is from about 1.4to about 2.2 g/mL. Any non-polar solvent with this density will suffice(i.e., chloroform, carbon tetrachloride, pentachloroethane). Preferably,the density of the solvent is about 1.6 to about 2.0 g/mL so that afteraddition of adhesives and an initiator, the density of the resultingsolution or dispersion matches the density of a 40-60 μM silicaparticle. A preferred solvent is pentachloroethane. Pentachloroethanehas the advantages of effective density (1.685 g/mL), low vapor pressure(no rapid evaporation when working with suspension), and clarity (easierto monitor the suspension behavior).

When heated to an effective temperature, the silazane and siloxanecross-link with themselves and each other. Generally, the Si—H groups onthe siloxane polymer react with the vinyl, Si—H and N—H groups of thesilazane oligomer. Further, both the silazane and the siloxane have theability to react with themselves. As a result, a “webbed” type formationis created which bonds to the polyolefin (e.g., polypropylene),acrylate, methacrylate, stainless steel or Teflon pipette tip walls aswell as physically entraps the particulate adsorptive material. Thecross-linking has the effect of tying up substantially 100% of the bondsof the silazane and siloxane such that substantially no reactive groupsare available to interact with an analyte, such as a protein.

The temperature range effective to cross-link the silazane and siloxaneto form the silazane/siloxane matrix is from about 25° C. to 250° C. Inpreparation of an adsorptive bed as a plug in a pipette tip, thetemperature range is more typically from about 60° C. to about 250° C.

To effect cross-linking of the adhesive and to remove the solvent, thepipette tips are preferably placed in an oven and heated to betweenabout 130° C. and about 145° C., most preferably at a rate of from about12° C./min to about 20° C./min. The ramp rate dictates the rate ofevaporation of the solvent. Generally, for this embodiment of theinvention, the faster the evaporation rate the larger the interstitialspaces that are formed. A preferred ramp rate is about 16° C./min. Atrates less than about 12° C./min, the interstitial pores that are formedin the adhesive structure during the heating process are small, therebyrestricting flow rates. In contrast, ramp rates greater than about 20°C./min can lead to particle shifting thereby creating macrochannels(large interstitial pores). Depending on the solvent and othervariables, adsorbent bed disruption may result from evaporation at ramprates above about 24° C./min.

FIG. 3 depicts the micropipette tip morphology of the present inventionbefore use and FIG. 4 depicts the morphology after use. The sphericalparticles evident from the photographs show the silica-based adsorptiveparticles forming part of the adsorptive bed. It should be noted thatthe adsorptive bed is substantially in the same condition after use asbefore use. Therefore, it may be concluded that, unlike somecommercially available pipette tips, the interior/middle of theadsorbent bed does not break or fracture during the pre-wet oradsorptive process. The pipette tips of the present invention possessmany (about 100) interstitial space channels which allow for fast flowof the sample through the adsorbent beds and tips. The resultingdispersed flow also allows for superior adsorptive particle/analytecontact, thereby increasing the capacity. In some cases, the capacity isthree times that of pipette tips that have been commercially available.Further, the quantity of silica in the pipette tips of the presentapplication is approximately from about 300 to about 600 μg, which isgreater than that of tips commonly used in the art. The photographsdepicting the present invention show that (a) the 30-75 μM adsorptiveparticles provide uniform, effective interstitial space resulting inexcellent flows; (b) the adhesives of the present invention provide anadsorptive bed with no significant breakage; and (c) capacity isincreased since the amount of silica may be increased. The adsorbentplug comprises few if any “macrochannels,” the presence of which mayotherwise lead to rapid flow of fluid sample through bed, precludingadequate contact between analyte and adsorbent particles. Preferably,the bed is substantially free of such macrochannels. It may be notedthat undesirable by-passing of the adsorbent particles can also resultfrom partial breakage during formation of the bed, an effect that isalso substantially avoided in the formation of the adsorptive mass inthe tip according to the methods described hereinabove. Thus, the plugformed in the tip has a high adsorptive capacity, and is not subject tocontamination such as would compromise sample preparation or analysis.

The suspension used in preparing the adsorptive plug in the tippreferably comprises about 1.5% to 5%, preferably about 1.8% to about2.5%, siloxane, between about 2% and about 7.5%, preferably betweenabout 2% and about 3%, silazane, between about 0.01% and about 1%,preferably between about 0.02% and about 0.75%, initiator, and betweenabout 5% and about 30%, preferably between about 6% and about 20%,adsorptive material. In various embodiments, the polysiloxane content isin the range of 60-100 mg/mL; the polysilazane content is in the rangeof 60-400 mg/mL; and the solvent represents approximately 75% to 85% ofthe total weight of the suspension. An exemplary and especiallyadvantageous suspension may comprise approximately: 375 mg/mL ofC₁₈-silica; 70 mg/mL of siloxane, preferably polydimethyl siloxane; 84mg/mL of polysilazane; and 4.0 mg/mL of initiator, preferably dicumylperoxide. The ratio of polysiloxane polymer to polysilazane polymer isfrom about 1.0 to 0.5 to about 1.0 to about 10.0, more preferably fromabout 1 to about 1.2 to about 1 to about 5. For example, the compositionof the initial suspension may comprise about 70 mg/mL of polysiloxaneand about 84 mg/mL of polysilazane.

Although the suspension may be cured in various atmospheres, it ispreferably cured in air (i.e., oxygen). Air is preferred because theweight loss of the silazane is minimized, as described above, and thetwo polymer adhesives react effectively as two polymers with littlerestructuring of the silazane. By proper selection of solvent, theinitial suspension may remain stable for at least 4 hours, and often forat least 48 hours.

Permeability of the polysilazane/polysiloxane matrix has been foundsuperior to the permeability of a matrix formed from either of thecomponents individually. It is theorized that the improved permeabilityis the result of shrinkage of the entire adhesive mass during heating.The silazane forms a polymer/hard adhesive film around the siloxane andthe particulate adsorbent material(s). During the cure process, it isbelieved that the silazane physically pulls the siloxane out of theinterstitial spaces and contracts the adhesive moiety around theparticles. Both adhesives are impermeable to the aqueous/liquid samplecontaining the analyte.

Other characteristics of the matrix include the fact that swelling ofthe polysiloxane occurs without the silazane, but only insignificantswelling occurs in with the presence of the silazane. Thus, thecombination decreases the overall swelling that occurs with in thepresence of the polysiloxane alone.

In the pipette tips application of the current embodiment, thepolysilazane/polysiloxane matrix should be present in an amountsufficient to produce a stabilized adsorbent bed, but not restrict theflow of the sample. The interstitial channels allow access of the sampleanalytes to the pores of the particulate adsorptive material and alsoallow for effective transport of the sample through the bed. The matrixdescribed by this invention has an advantage of effectively adhering theadsorbent bed, while not blocking access of an analyte to the adsorptionsurface of the pores of the particulate adsorbent material, where theadsorbent is porous, access to the adsorbent pores is also preserved.Minimizing adsorbent pore blockage results in increased opportunity forthe target analyte to have contact with the adsorptive surfaces interiorto the adsorptive particle and increased yields of the target analyte.By preserving access to the external surfaces, yields are also enhancedwhere non-porous adsorbents are used.

Consideration governing selection of an adsorbent for the pipette plugare comparable to those discussed for any of the above embodiments.Thus, particulate adsorbent materials include nucleophilic,electrophilic, or neutral materials. Exemplary particulate adsorptivematerials may be selected from carbon, organic polymers, silicas,zeolites, aluminas, metal or ceramic powders. Further adsorbentmaterials include styrene, DVB, ion-exchange resins, enzymes, andinteractive/biological reactive materials (i.e., bonded antibodies,antigens, etc.). In a preferred embodiment, the particulate adsorptivematerial is C₁₈-silica.

The particle size distribution of the particulate adsorptive materialfor this embodiment is such that at least 50% by weight thereof has aparticle size from about 1 nanometer to about 1 millimeter. Preferablyabout 95% by weight of the particulate adsorptive material has aparticle size from about 5 to about 75 microns. It is further preferredthat about 95% by weight of the particulate adsorptive material have aparticle size from about 40 to about 60 microns.

Selection of an initiator for cross-linking of the silazane and siloxaneis guided by the nature of the cross-linking groups and the method ofcross-linking desired. For example, a peroxide may be used in aneffective amount for vinyl functional polymers. The reactivity of vinylfunctional polymers is utilized in two major regimes. Vinyl terminatedpolymers are employed in addition cure systems. The bond formingchemistry is the platinum catalyzed hydrosilylation which proceedsaccording to the following chemical equation:

Vinylmethylsiloxane copolymers and vinyl T-structure fluids are mostlyemployed in peroxide activated cure systems which involve peroxideinduced free radical coupling between vinyl and methyl groups.Concomitant and subsequent reactions take place among methyl groups andbetween cross-link sites and methyl groups. The initial cross-linkingreaction is depicted in the following equation:

In a preferred embodiment of the present invention, the cross-linking isinitiated via a peroxide activated cure. A person skilled in the artwould recognize that various peroxides may be suitable for thecross-linking reaction described herein. In a more preferred embodiment,the initiator is a peroxide selected from the group consisting of2,5-Bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne, dicumyl peroxide,1,1-Bis-(tert-butylperoxy)-3,3,5-trimethylcyclohexane, and2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane. FIG. 6 depicts therelationship between cure time (minutes) and temperature (° C.) withdifferent peroxides for conversion of the fluid polysilazane oligomer tothe cross-linked polymer. In a most preferred embodiment the initiatoris dicumyl peroxide.

In addition to vinyl groups, other functional groups may be involved inthe cross-linking process. For example, hydride (Si—H) functional groupsundergo three main classes of reactivity (general reactions are shownbelow): hydrosilation, dehydrogenative coupling and hydride transfer.These general reactions may play a role in the cross-linking of thesiloxane and silazane with each other and themselves.

Hydrosilylation may occur according to the following general reaction:

The hydrosilylation of vinyl functional siloxanes, for example, byhydride functional siloxanes is the bases of addition cure chemistryused in 2-part RTVs and LTVs. The preferred catalysts for the reactionsare platinum complexes.

Dehydrogenative coupling may occur according to the following generalreaction:

In dehydrogenative coupling, hydroxyl functional materials react withhydride functional siloxanes, for example, in the presence ofbis(2-ethylhexanoate)tin, dibutyldilauryltin, zinc octoate, iron octoateor a variety of other metal salt catalysts.

Reduction (hydride transfer) may occur according to the followinggeneral reaction:

Reduction reactions may be catalyzed by Pd⁰ of dibutyltinoxide. Thechoice of reaction conditions leads to chemoselective reduction, e.g.,allyl reductions in the presence of ketones and aldehydes.

Silanol (Si—OH) functional polymers may render the siloxane or silazanesusceptible to condensation under both mild acid and base conditions.Low molecular weight silanol fluids are generally produced bykinetically controlled hydrolysis of chlorosilanes. Higher molecularweight fluids can be prepared by equilibrating low molecular weightsilanol fluids with cyclics, equilibrium polymerization of cyclics withwater under pressure or methods of polymerization that involvehydrolyzable end caps such as methoxy groups. As one skilled in the artwill appreciate, methods such as moisture curing may be used for thistype of functional groups. Common moisture cure systems include acetoxy,enoxy, oxime, alkoxy and amine functional groups and may proceed asoutlined in the following general reactions:

Further, aminofunctional silicones (i.e., Si—CH₂CH₂CH₂NH₂) have a broadarray of applications as a result of their chemical reactivity, theirability to form hydrogen bonds and, particularly in the case ofdiamines, their chelating ability. Additional reactivity can be builtinto aminoalkyl groups in the form of alkoxy groups.

Epoxy functional silicones

undergo cross-linking reactions with amines. The ring-strainedepoxycyclohexyl group is more reactive than the epoxypropoxy group andundergoes thermally or chemically induced reactions with nucleophilesincluding protic surfaces such as cellulosics. Epoxycyclohexylfunctional siloxanes may polymerize on UV exposure in the presence ofweak donor catalysts according to the following general reaction:

Carbinol (hydroxyl group bound to a carbon) terminated functionalsiloxanes contain primary hydroxyl groups which are linked to thesiloxane backbone by non-hydrolyzable transition groups. Frequently, atransition block of ethylene oxide or propylene oxide is used. Carbinolfunctional polydimethylsiloxanes may be reacted into polyurethanes,epoxies, polyesters and phenolics.

Methacrylate and acrylate functional siloxanes (shown below),

undergo the same reactions generally associated with methacrylates andacrylates, the most conspicuous being radical induced polymerization.These functional groups are also often utilized in UV cure systems.

Other functional groups that may be present as substituents on thesiloxane or silazane include isocyanate, carboxylate, mercapto,chloroalkyl, and anhydrides.

Although other formulae have been used, according to J. Fluid Mech. 370,79 (1998), the aspect ratio of the adsorptive beds is measured by thebed length divided by the average bed radius at midpoint of the bed asdetermined by the following formula:

${{aspect}\mspace{14mu} {ratio}} = \frac{L}{\left( {{r_{0}2} + {r_{0}1}} \right)/2}$

“L” is the bed length, “r₀1” is the first radius measurement, and “r₀2”is the second radius measurement. r₀1 may be measured at the top of thebed while r₀2 is measured at the bottom of the bed, nearest the pipetteorifice (see FIG. 1). The radius is generally measured in microns. Whenmeasured according to the formula recited above, the aspect ratio of thepipette tips may be anywhere from about 2 to about 40. A lower aspectratio may decrease retention time, but adsorption may be reduced becauseless adsorptive material is available for binding the desired analyte.On the other hand, higher aspect ratios may be beneficial by allowingfor increased contact time and available surface for contact between theadsorbent and analyte. Thus, for certain applications, the aspect ratiois preferably at least 11, more preferably at least 15, still morepreferably at least 20. For certain pipette tip applications, the aspectratio is preferably between about 10 and about 25. For certain otherapplications, the aspect ratio is preferably at least 2, more preferablyat least 5. For still other applications, the aspect ratio may betweenabout 2 and about 12, more preferably between about 3 and about 8. In anexemplary embodiment, the pipette tips described herein have a tiporifice of about 350 to about 750 μM and the total area percentage (thecross-sectional area presented by the projection of the first layer ofparticles onto the plane of the tip orifice) of particles at the tiporifice is about 90 to about 93% (see FIG. 2). Further, the total areapercentage of void spaces at the tip orifice is generally from about 7to about 10%.

While pipette tips represent a preferred application of thefluid-permeable adsorption mass of this invention, there are otheradvantageous applications. Other useful structures include wells,multi-well arrays, plastic and glass cavities, and sample preparationdevices. A solid phase adsorption device may comprise a fiber bearing anadsorptive coating comprising a matrix having a particulate adsorptivematerial lodged therein. For example, such a coating may be providedover the fiber of a solid phase microextraction device as described inPawliszyn U.S. Pat. No. 5,691,206, the entire disclosure of which isincorporated herein by reference. The matrix comprises an amorphousnon-glassy ceramic composition as described hereinabove. Optionally, theinterior of the syringe barrel illustrated in the Pawliszyn patentand/or the interior and exterior of the housing surrounding the fibermay have a passivation coating comprised of the same or similar ceramic.

According to a further alternative, a solid phase adsorptive device maycomprise a fluid-permeable adsorptive bed contained within a vessel orconduit. More particularly, the solid phase adsorptive device maycomprise a conduit or vessel having particulate adsorptive materialentrapped therewithin by a binder comprising a polysilazane polymer anda polysiloxane polymer. The solid phase adsorptive device may contain afluid-permeable mass which comprises the binder and particulateadsorbent material. Typically, the fluid-permeable mass has apermeability of about 5 to about 10 μL/second. Further, the inventioncontemplates the solid phase adsorptive device of the present embodimenthaving an adsorptive zone, which contains the particulate adsorbentmaterial, in a concentration of at least 0.2 g/cc. In a preferredembodiment, the particulate adsorbent is present in a concentrationbetween about 0.2 and about 0.5 g/cc. In one embodiment, the adsorptivezone is such that the surface area of said adsorptive material withinthe zone is at least about 10 m²/cc.

The present invention further contemplates a process for preparing afluid-permeable mass comprising a particulate adsorbent materialdispersed in a polymeric matrix comprising: preparing a dispersioncomprising the particulate adsorbent material in a liquid mediumcomprising a solvent, a polymerizable silazane and a polymerizationinitiator, the polymerizable silazane comprising a polysilazane monomer,a polysilazane oligomer, or a mixture thereof; and polymerizing thepolymerizable silazane to form said fluid-permeable mass.

Also contemplated by the present invention is a method for isolating atarget compound from a sample comprising a fluid medium containing saidcompound, the method comprising: drawing the sample into a vessel orconduit containing an adsorbent bed, the adsorbent bed comprisingparticulate adsorbent material dispersed in an adhesive matrix orentrapped by an adhesive binder; and allowing said target compound to beadsorbed to particles of said adsorbent material. The adhesive matrix orbinder comprises a polysilazane polymer and a polysiloxane polymer.

The following examples illustrate the invention.

EXAMPLE 1

A ⅛″ thick aluminum coupon was cleaned thoroughly with soap and waterremoving any surface debris with a steel wool pad. The aluminum samplewas then rinsed with distilled water and placed in an oven at 200° C.for approximately 10 minutes. A solution consisting of thermosetpolysilazane (2.5 g), dicumyl peroxide (0.05 g) and pentane (50 ml) wasloaded into a touch up spray gun (Badger Model 400). The aluminum couponwas removed from the oven and immediately sprayed creating a uniform,vulcanized coating on its surface. The sample was then placed in an ovenfor further curing to the preceramic state via an oven ramp at 200° C.for 10 minutes, then at 450° C. for 10 minutes. The film appearedhomogenous, crack free with no signs of delamination when studied undermagnification with a light microscope.

EXAMPLE 2

A ¾″ copper tube was cleaned thoroughly with soap and water removing anysurface debris with a steel wool pad. The copper sample was then rinsedwith distilled water and placed in an oven at 200° C. for approximately10 minutes. A solution consisting of thermoset polysilazane (2.5 g),dicumyl peroxide (0.05 g) and pentane (50 ml) was loaded into a touch upspray gun (Badger Model 400). The copper tube was removed from the ovenand immediately sprayed creating a uniform, vulcanized coating on itssurface. The sample was then placed in an oven equipped with a heliumpurge vessel for further curing to the preceramic state via an oven rampat 200° C. for 10 minutes, then at 450° C. for 10 minutes. The filmappeared homogenous, crack free with no signs of delamination whenstudied under magnification with a light microscope.

EXAMPLE 3

The inner diameter of a 4 mm HPLC column was cleaned thoroughly withmethylene chloride and permitted to air dry. A solution consisting ofthermoset polysilazane (2.5 g), dicumyl peroxide (0.05 g) and pentane(50 ml) was prepared as the coating solution. A lint free applicator wasdipped in the solution and whisked to remove excess material. The innersurface of the column was painted with the applicator resulting in athin even coating. The column was then placed in an oven in the uprightposition for curing to the preceramic state via an oven ramp at 200° C.for 10 minutes, then at 450° C. for 10 minutes. The coating wassubjected to low pH mobile phase conditions without degradation.

EXAMPLE 4

Acid washed borosilicate wool (10 g) was saturated with a solution ofthermoset polysilazane (1 g), dicumyl peroxide (0.02 g), and pentane(500 ml). Excess solution was removed from the wool before drying with anitrogen purge. The wool was transferred to an oven for curing to thepreceramic state via an oven ramp at 200° C. for 10 minutes, then at450° C. for 10 minutes. This treated wool was found to significantlyreduce pesticide breakdown when packed in a gas chromatographic inletsleeve.

EXAMPLE 5

Surfaces of a steel powder-dispensing device were cleaned thoroughlywith methylene chloride and permitted to air dry. A solution consistingof thermoset polysilazane (2.5 g), dicumyl peroxide (0.05 g) and pentane(50 ml) was prepared as the coating solution. A lint free applicator wasdipped in the solution and whisked to remove excess material. Thesurfaces of the filling device were painted with the applicatorresulting in a thin even coating. The devices were placed in an oven forcuring to the preceramic state via an oven ramp at 200° C. for 10minutes, then at 450° C. for 30 minutes. The coating was subjected topowders containing silver nitrate for extended times withoutdegradation.

EXAMPLE 6

Stainless steel frits (2 μm pore size) used commonly in HPLC columnswere cleaned thoroughly with methylene chloride and permitted to airdry. A solution consisting of thermoset polysilazane (2.5 g), dicumylperoxide (0.05 g) and pentane (50 ml) was prepared as the coatingsolution. Multiple frits were submerged in the coating solution using acylindrical glass vial. Excess solution was decanted, the vial wasflushed with a nitrogen purge in order to purge excess solution from thepores of the frit. The frits were placed in an oven for curing to thepreceramic state via an oven ramp of 200° C. hold 10 minutes, then 450°C. hold 30 minutes. The frits were used in the preparation of 4 mm i.d.HPLC columns for the analysis of peptide materials resulting in normalmobile phase flow rates and excellent surface inertness.

EXAMPLE 7

A 10 μl Hamilton syringe needle was coated on its interior by pulling asolution of thermoset polysilazane (1 g), dicumyl peroxide (0.02 g) andpentane (50 ml) utilizing the plunger of the syringe. The plunger wasdepressed expelling the coating solution and removed to allow a lightnitrogen purge down the length of the barrel to remove excess solution.The exterior of the needle was dip coated before the syringe needle wassuspended in a small barrel heater for 25 minutes at a temperature of400° C. The syringe was found to be in perfect working order after theabove treatment.

EXAMPLE 8

A solventless suspension of 2-3 μm, 6-2000 Å pore size Carboxen 1006(Supelco Corporation) (4 g), thermoset polysilazane (1 g), and dicumylperoxide (0.08 g) was prepared and shaken vigorously. A few drops ofthis formulation were placed on a glass microscope slide. A nitinolfiber was passed thru the droplet horizontally then rolled on a cleansection of slide to remove excess material. The coated fiber was heatedfor approximately 15 seconds with an industrial heat gun to cure thepolysilazane material in creation of a polymeric binder. The fiber wasthen recoated three additional times to create a 40 μm layer of boundadsorbent. The fiber was suspended in a small barrel heater equippedwith an inert gas purge in which it was cured to the preceramic state at400° C. for 10 minutes. The fiber was found to extract and desorb avariety of organic compounds with no sign of adsorbent pore blockage.The polysilazane binder resisted cracking and showed no signs ofdelamination from the nitinol wire.

EXAMPLE 9

5 μm, 120 Å pore size silica gel (Diasogel) (5 g) was saturated with a20 ml solution of thermoset polysilazane (1 g), dicumyl peroxide (0.02g), and pentane (50 ml). The excess solvent was allowed to evaporate ina fume hood. The silica was placed in an oven where the coating wastransformed to the preceramic state via an oven ramp of 200° C. hold 10minutes, then 450° C. hold 30 minutes. The silica gel was chemicallybonded with octadecyl silane and used in the preparation of an HPLCcolumn. A standard reversed phase test mix revealed near equivalentchromatography to that of a control octadecyl silane HPLC column. Carbonloadings on the polysilazane coated material were also found to beequivalent.

EXAMPLE 10

A suspension of 1-10 μm, 500-600 Å pore size Carbopack Z (SupelcoCorporation) (670 mg), thermoset polysilazane (3 g), dicumyl peroxide(0.06 g) and pentane (15 ml) was prepared and shaken vigorously. Thesuspension was loaded into a Badger 400 touch up sprayer used in coatingthe fibers to 20-30 μm thickness. The fiber was suspended in a smallbarrel heater equipped with an inert gas purge in which it was cured tothe preceramic state at 400° C. for 10 minutes. The fiber was found toextract and desorb a variety Arochlor congeners with no sign ofadsorbent pore blockage. The polysilazane binder resisted cracking andshowed no signs of delamination from the stainless steel wire.

EXAMPLE 11

A suspension of 2-3 μm, 6-2000 Å pore size Carboxen 1006 (SulpelcoCorporation) (250 mg), thermoset polysilazane (500 mg), dicumyl peroxide(25 mg) and methylene chloride (1 ml) was prepared and shakenvigorously. One end of a 15 cm long 0.25 mm i.d. fused silica tube wasplugged and raised slowly into a tube furnace heated at 200° C. The tubewas then connected to a gas chromatograph injection port and heated to360° C. for 10 minutes with a helium purge. A flexible layer ofentrapped bound particles resulted inside the fused silica tube.

EXAMPLE 12

A chloroform suspension containing 50 μm, 200 Å pore size octadecylsilylated silica (Supelco Corporation), thermoset polysilazane,polydimethyl siloxane and dicumyl peroxide was prepared and shakenvigorously. The suspension was drawn into pipette tips, placed in afreeze dryer at 0° C. for approximately 10 minutes then transferred toan oven for vulcanization at 145° C. The polysilazane additive was foundto crystallize while under freeze drying conditions preventing gravitysettling of the silica particles. Beds prepared with this methodprovided consistent solvent flow rates, mechanical stability and highextraction efficiency for various biomolecules.

EXAMPLE 13

Surfaces of a tool steel-dispensing device were sandblasted to removeoxides and surface impurities. The devices were blown clean with anitrogen purge in order to remove debris before coating. A suspensionconsisting of thermoset polysilazane (5 g), 3 um zirconium powder (1 g)in methylene chloride (5 ml) was prepared for coating. The suspensionwas shaken vigorously then brush coated on the dispensing device with alint free applicator. The devices were placed in an oven, which wasrapidly heated to 450° C. for a period of 30 minutes then cooled slowly.The resulting coating provided extended oxidation and abrasionresistance to acidic silica powders.

EXAMPLE 14

15 meter lengths of 0.53 mm internal diameter 316 stainless steel tubeswere flushed with a coating solution (2 ml) composed of thermosetpolysilazane (10 g), dicumyl peroxide (0.2 g), dissolved in pentane (50ml). The flush was approximately 4 p.s.i. nitrogen pressure. The tubeswere allowed to purge for 30 minutes then placed in an oven at 200° C.for 10 minutes and 450° C. for 30 minutes. The coated columns weretested for inertness as a transfer line between a gas chromatographicinjection port system and an inert methyl silicone capillary columnconnected to a PDD detector in helium ionization mode. Trace amounts ofsulfur gases and water vapor were transferred without adsorption to thecapillary column. The results are shown in FIG. 8.

EXAMPLE 15

A solution of thermoset polysilazane (1 g), dicumyl peroxide (0.02 g)dissolved in pentane (50 ml) was coated on a potassium bromide sampleplate. An infrared spectrum of the film was recorded after heattreatment at 200° C. and 450° C. in an air filled oven. Absorption bandsassociated with silazane, silicon hydride and vinyl functional groupsdisappeared after the high temperature cure. The results are shown inFIG. 10.

EXAMPLE 16

A solution consisting of thermoset polysilazane (2.5 g), dicumylperoxide (0.05 g) and pentane (50 ml) was prepared. A lint freeapplicator was used to apply a single coat of material on a 1/16″stainless steel panel. The panel was heated for 10 minutes at 200° C.then 30 minutes at 450° C. in air. Using EDS, a sputter profile of theresulting coated surface revealed a ceramic layer of approximately 3000angstroms containing residual carbon and nitrogen species in apredominately silicon and oxygen ceramic matrix. The results are shownin FIG. 9.

EXAMPLE 17

Polydimethyl siloxane (70 mg/ml), thermoset polysilazane (84 mg/ml),dicumyl peroxide (4.0 mg/ml), and pentachloroethane were added to 7 mlvial and mixed for 1.0 hours using a vortex mixer. This mixture was thenadded to a second 7 ml vial containing 50-60 μM 200 Å pore silica (375mg/ml) and mixed for 15 minutes on a vortex mixer. The resultingsuspension was chilled overnight at 5-10° C. The suspension was thenallowed to reach room temperature for 30 minutes followed by mixing onvortex mixer for 10 minutes.

The pipette tips were prepared using a 10 (or 20 μl) pipetter set to a3.0 μl draw volume. 3.0 μl of the suspension was drawn into each tip.The tips were placed in a rack and heated in an oven to 145° C. at 16°C./minute, hold at 145° C. for 10 minutes. The oven was allowed to coolbelow 60° C. and the tips removed.

EXAMPLE 18

The samples for the Carboxen-1006 DFT plot (FIG. 11A) were prepared asfollows. Initially, the non-bonded Carboxen-1006 was tested usingporosimetry. The bonded Carboxen-1006 was prepared in a 100 milliliterbeaker using a suspension of carbon and adhesive suspended indichloromethane. The ratio of carbon to adhesive was 1:4. The suspensionwas then dried in a convection oven at ambient until the carbon powderwas free-flowing, and the powder was subsequently bonded at 350° C. Theresulting mass of carbon/adhesive was then tested using porosimetry.

The samples for the silica DFT plot were prepared using a suspensionprocess as described in Example 17 (i.e., 70 mg/mL siloxane, 84 mg/mLsilazane and 375 mg/mL of 300 Å C18 bonded silica), but instead offilling tips, the suspension was placed in a 100 milliliter beaker andbonded at 145° C. for 10 minutes. The bonded silica mass was removedfrom the beaker by scraping/dislodging the mass and analyzed usingporosimetry.

1. A fluid-permeable mass comprising a particulate adsorbent materialdispersed in a matrix comprising a polysilazane polymer and apolysiloxane polymer.
 2. A fluid-permeable mass as set forth in claim 1having a permeability of about 5 to about 20 μL/second.
 3. Afluid-permeable mass as set forth claim 1 wherein said matrix issubstantially not irreversibly adsorptive of an analyte or other targetcompound that is adsorbed by said particulate adsorptive material.
 4. Afluid-permeable mass as set forth in claim 1 and contained within aconduit or vessel, said matrix being adhered to an interior wall of saidconduit or vessel.
 5. A fluid-permeable mass as set forth in claim 1containing at least about 40% by weight of said particulate adsorptivematerial.
 6. A fluid-permeable mass as set forth in claim 1 wherein theB.E.T. surface area of said particulate adsorptive material is at leastabout 1 m²/g.
 7. A fluid-permeable mass as set forth in claim 1 whereinthe concentration of said adsorptive material is such that the surfacearea thereof is at least about 0.1 per cc of said mass.
 8. Afluid-permeable mass as set forth in claim 1 wherein said polysiloxanepolymer contains repeating Si—H groups at from about 1% to about 10%intervals.
 9. A fluid-permeable mass as set forth in claim 1 whereinsaid polysiloxane polymer comprises siloxane repeating units of theformula:

wherein R₃ is hydrogen, substituted or unsubstituted hydrocarbyl,alkoxy, aryloxy, nitro, cyano, amino, hydroxy, or an —O—Si≡ moiety; andR₄ is hydrogen, methacryl, C₁₋₂₀ alkyl, C₂₋₂₀ alkenyl, fluoroalkyl,carbonyl, carbinol, glycidyl, straight, branched or cyclic—(CH₂—O—CH₂)_(n), and aryl optionally substituted with C₁₋₆ alkyl,fluoro, chloro, cyano or aryl.
 10. A fluid-permeable mass as set forthin claim 1 wherein said polysilazane polymer comprises silazanerepeating units having the formula:

wherein: is selected from the group consisting of hydrogen, vinyl,alkyl, hydroxy, alkoxy, amino, alkylamino, mercapto, acetoxy, halo,hydroxyalkyl, dimethylamino, oxime, isocyanate, CH₂Q-(OCH₂CH₂)_(n)OH,

R₂ is selected from the group consisting of methacryl, C₁₋₂₀ alkyl,C₂₋₂₀ alkenyl, fluoroalkyl, carbonyl, carbinol, glycidyl, straight,branched or cyclic —(CH₂—O—CH₂)_(n), and aryl optionally substitutedwith C₁₋₆ alkyl, fluoro, chloro, cyano or aryl; Q is C₁₋₈ alkyl; and nis 1 to about
 20. 11. A fluid-permeable mass as set forth in claim 10wherein said oligomer has the formula:

wherein R is H or —CH═CH₂ and n is 1 to
 20. 12. A fluid-permeable massas set forth in claim 1 wherein said particulate adsorptive material isselected from the group consisting of carbon, organic polymers, silicas,zeolites, aluminas, metal or ceramic powders.
 13. A fluid-permeable massas set forth in claim 1 wherein at least 85% of the pore volume of saidparticulate adsorptive material is constituted of pores having a poresize between about 2.5 Å and about 10,000 Å.
 14. A fluid-permeable massas set forth in claim 13 wherein at least 85% of the pore volume of saidadsorptive material is constituted of pores having a pore size betweenabout 100 Å and about 300 Å.
 15. A fluid-permeable mass as set forth inclaim 1 wherein the ratio of polysiloxane polymer to polysilazanepolymer is about 1.0 to 0.5 to about 1.0 to 10.0.